The present disclosure relates to paper manufacturing and processing. The present disclosure also relates to methods and systems for reducing, eliminating, or preventing folding or wrinkling prior to, or as part of, winding or calendering processes.
During paper manufacturing and processing, a paper web or sheet can pass through one or more calendering rolls to control the thickness, bulk, and/or surface properties of the web. In some instances, calendering can involve passing a continuous web between a pair of continuously-turning rollers having a pattern or texture that is imparted to the web as the web passes between the calendering rollers. In other instances, calendering can involve passing a continuous web between a pair of continuously-turning rollers to impart smoothness or uniformity to the surface of the web as the web passes between the calendering rollers.
The web can also be wound onto a large roll or reel one or more times during the process. The winding process involves continuously and repeatedly turning a large roll about a central shaft, drawing the paper sheet onto the roll as the sheet leaves another component of the paper machine. For example, the winding process may occur as the web exits a drying section of the paper machine or as the web exits the calendering rollers. The web may also be rewound following a first winding section in one or more subsequent roll-to-roll winding sections.
Paper manufacturing and processing typically involves moving the paper product at very high speeds. Because of these high speeds, defects may occur in the web. For example, the paper product may experience wrinkles, folds, curling, edge flutter, and the like. Certain paper processing operations, such as calendering and winding, increase the likelihood of these defects. For example, as the web passes from a dryer to the calendering rollers, folds and wrinkles form as the web is transported to the calendering rollers. These folds and wrinkles can be compressed by the calendering rollers, creating folds, wrinkles, or other defects in the web and also defects in the calendered pattern imparted by the rollers. These folds, wrinkles, and pattern defects are types of “visual defects” that are seen in the final paper web.
Various methods have been employed in order to control a paper web to avoid such defects. For example, mechanical spreading has been used, which requires a web to be dragged over bowed elements. However, such dragging action typically has negative effects on sheet properties. Such prior methods are not ideal, typically having negative effects on sheet properties, and are not as effective at higher speeds. They also do not sufficiently reduce folding and wrinkling in the calendering and winding processes, resulting in visual defects in the final product.
Accordingly, a need exists for an improved method of reducing, preventing, or eliminating defects in the papermaking process that does not suffer from the problems discussed above. The present disclosure provides advantages over prior mechanical spreading means by applying air to directly spread the web via an air spreader, such as without dragging the web over various elements. The application of a foil on the opposite side of the web may also provide additional advantages to support the web as the gas is expelled against it. The air spreader described herein also provides certain advantages to decrease or reduce wrinkles and folds in the web as it proceeds to, for example, calendering rollers, embossing rollers, or winding rollers, which prevents visual defects, such as wrinkles, folds, or pattern defects in the final web.